1. Field of the Invention
The present invention relates to a signal processing method for an image capturing apparatus, and an image capturing apparatus. In particular, the present invention relates to a technique for remedying problems due to insufficient transfer efficiency of CCD (charge coupled devices) image capturing elements.
2. Description of the Related Art
Conventionally, image capturing apparatuses using CCD image capturing elements, such as electronic cameras, digital cameras and camera-equipped mobile phones, have been developed. When performing image capturing using such an image capturing apparatus, signal charges are accumulated in each pixel of a CCD image capturing element according to exposure time. Signal charges accumulated in each pixel are transferred from a vertical transfer path to a horizontal transfer path, and are outputted to an image processing circuit.
Signal charges accumulated in each pixel are sequentially transferred via potential wells respectively formed at each transfer element of each transfer path. At this point, the signal charges are not completely transferred to the next transfer element, and a small portion is left behind. The ratio of the charges transferred to the next well to the charges that were in the original well is called transfer efficiency. When the transfer efficiency is reduced, crosstalk between adjacent pixels increase, and various problems such as image deterioration (deterioration of color reproducibility or resolution) occur.
In consideration of the above problems, for instance, a signal correction apparatus for distance measuring CCDs, arranged so as to correct image signal distortion due to transfer errors in order to eliminate inadequate distance measurement, is disclosed in Japanese Patent Application Laid-Open No. 7-146139. In addition, a signal processing method in which a sum of vertical transfer remaining amounts of image sensors lined in a TDI (time delay integration) stage direction is obtained in advance from the vertical transfer efficiency of a TDI image sensor, the sum is then subtracted from an output of the TDI image sensor upon performing image capturing of a sample by the TDI image sensor, and the output after subtraction is used to perform image processing, is disclosed in Japanese Patent Application Laid-Open No. 2004-295709.